It has long been a desirable goal to add sensitive ingredients such as enzymes, bleaches and/or bleach catalysts to enhance the cleaning efficacy of detergent products, particularly liquid detergent products. Liquid detergents, however, often provide a hostile environment to these sensitive ingredients. For example, enzymes are subject to attack by anionic actives, high pH conditions, and/or by other enzymes. Bleaches, in particular peracid bleaches such as are taught in U.S. Pat. No. 4,909,953, are known to be particularly harsh on enzyme components.
One method of protecting sensitive components from their surrounding harsh environment is by encapsulation of the ingredients. Further, encapsulation allows sensitive and possibly harmful materials to be handled more safely.
The capsules of the present invention are prepared by combining the sensitive component/hydrophobe mixture (in embodiment of invention where hydrophobe is used) and a cross-linking polymer, and forming atomized droplets from a nozzle followed by curing the droplets in a hardening solution to form hardened capsules. The sensitive component/hydrophobe mixture is prepared by dispersing the sensitive component within the hydrophobic barrier material and then forming droplets or cores out of this material to be coated by the cross-linking polymer. This type of capsules where a barrier material and sensitive material form the core within can exist in two morphologies. The first involves a single core of structured hydrophobe (containing the sensitive component) coated with the cross-linking polymer gel. This is commonly known as a core/shell capsule. The second constitutes a number of cores of structured hydrophobe (containing the sensitive component) which are dispersed within the cross-linking polymer gel. This is commonly known as a matrix capsule.
It should be noted, that in a separate embodiment, the capsules of the present invention also apply to cases where a hydrophobic barrier material may not be a component of the capsules. In such cases, the capsules are prepared by combining the sensitive component within a cross-linking polymer and forming atomized droplets from a nozzle followed by curing the droplets in a hardening solution to form hardened capsules.
Prior arts teach various methods or processes of encapsulating materials. Some of these methods are cited in U.S. Pat. No. 4,898,781 to Onouchi et al. These include preparing a water-containing solution of a hydrophilic substance, a supporting substance, and a polyvinyl alcohol substance, and causing this solution to fall in the form of minute drops into a cross-linking agent, or into a hydrophobic agent, or into a dehydrating agent, or heating the resultant mixture under a vacuum or by spray drying thereby allowing the polyvinyl alcohol to form a coat. This patent also cites a method wherein the water-containing supporting substance having the hydrophilic substance and the cross-linking agent dissolved therein are caused to be spouted out of the central orifice of a two-wall coaxial circular nozzle of a spray drier, and at the same time, an aqueous 15% polyvinyl alcohol or modified polyvinyl alcohol solution is caused to be spouted out of the peripheral orifice of the same circular nozzle, and then dehydrating the resulting mixture as with dry air. Another cited method is by dissolving or dispersing a hydrophilic substance in a supporting substance which fails to show flowability in a dry state, spray drying the resultant mixture to form substantially spherical minute drops, and then coating the minute drops with aqueous polyvinyl alcohol or modified polyvinyl alcohol solution. The three encapsulation processes described above can be simply stated as: 1) drop-wise addition of the mixture of active containing solution and polyvinyl alcohol material into a hardening agent (a "batch" process); 2) spray drying of the aforementioned mixture using a two wall coaxial circular nozzle: and 3) spray drying of the active containing solution followed by coating of the resultant droplets with polyvinyl alcohol material. There are some processing concerns about these three prior techniques. The first method is a batch process and it can cause aggregation of encapsulates when fresh droplets come in contact with incompletely hardened droplets or with completely hardened capsules in the container containing the hardening liquid. The second and third methods entail spray drying process which is not feasible for temperature sensitive ingredients, and which may also pose a safety risk in terms of containing the fine dusts or aerosols of possibly harmful ingredients formed during spray drying.
Accordingly, it is an object of the invention to prepare the capsules of the invention in a continuous rather than batch process.
It is a further object of the invention to contain, in a closed system, possibly harmful aerosols formed during processing.
A further object of the invention is to prevent aggregation of capsules which occurs in the batch process when many capsules are formed in a container containing the hardening fluid.
Another object of the invention is to relieve these capsules of high shear and agitation required to renew the collection bath surface in the batch process.
Another objective of the invention is to avoid generation of dry, fine dust of possibly harmful ingredients during processing in a spray drying process.
These and other objectives are met by utilizing the process described below.